It has been proposed that the effects of ethanol in the CNS are mediated by perturbation of neuronal membrane lipid structure, and that resistance of the membranes to ethanol's effects is involved in ethanol tolerance. The function of enzymes embedded in cell membranes is influenced by the surrounding lipids, and measurement of the temperature dependence of enzyme activity (Arrhenius plots) is thought to provide an indication of the physical state of neuronal membrane lipids. We have demonstrated that, in ethanol-treated animals, there is a change in the lipid-dependent properties of neuronal Na+, K+ ATPase. In order to determine whether this change is related to ethanol tolerance, we now propose to measure enzyme activity during the acquisition and dissipation of tolerance in several strains of mice (which acquire tolerance of different rates). Furthermore, we will alter the rates of acquisition and dissipation of tolerance with neurotoxin and vasopressin treatment, and assess lipid-dependent enzyme activity. If the changes in neuronal membrane properties reflected in enzyme activity are determinants of tolerance, then their appearance and disappearance should parallel those of behavioral tolerance. The activity of two enzymes, Na+ K+ ATPase, and 5'-necleotidase, which are located in different areas of the neuronal membrane, will be assessed. To further determine the importance of lipid properties in the observed changes in enzyme activity, delipidation and reconstitution of Na+, K+ ATPase activity from control and ethanol-tolerant animals will be performed.